Isoproterenol induced fatty change in rat myocardium: freeze fracture study of the sarcolemma at sites of lipid droplet-membrane appositions

Abstract

Twenty four hours following subcutaneous administration of cardiotoxic doses (85 mg/kg body weight) of isoproterenol (ISO) to male Wistar rats, we observed accumulation of fat droplets in surviving cardiac muscle cells. This finding is consistent with the well established effect of ISO, a beta-receptor stimulant synthetic catecholamine, on lipid metabolism. On thin section electron microscopy lipid droplets were numerous in all surviving cardiac muscle cells, many of them located in close apposition to the sarcolemmal membrane. Freeze fracture electron microscopy revealed at sites of lipid droplet-membrane appositions bulging areas of the sarcolemmal membrane. The plane of fracturing interrupted frequently these bulging areas leaving irregular holes in membrane faces and visualizing the underlying lipid droplets. Intramembrane particles were always uniformly distributed in bulging membrane faces and around interrupted areas suggesting that holes on the sarcolemmal membrane resulted from physical properties of the membrane cleavage and were not related to lipid droplet-membrane fusion.